Electronic cigarette

ABSTRACT

This electronic cigarette ( 1 ) comprises: —a heating element ( 10 ) able to vapourize a substrate during a smoking period; —means ( 30 ) for measuring an approximation (AUIOMESOO, UIOMESOO) of a characteristic of the voltage (U10(t)) across the terminals of the heating element ( 10 ) during this smoking period, said approximation being measured across the terminals (BI, B2) of a circuit ( 500 ) no component of which exhibits intrinsic characteristics not disturbed by the inhalations; —means ( 30 ) of estimating an approximation (AU10TH(t), UIO-m(t)) of said characteristic of the voltage (U10(t)) across the terminals of the heating element ( 10 ) in the absence of inhalation during said smoking period; means ( 30 ) of calculating an intensity (F) representative of the intensity of the inhalations during said smoking period on the basis of an integration of the difference between said approximations during said smoking period; and —means ( 30 ) of estimating the said quantity of substrate vapourized by the heating element at least on the basis of said intensity.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/120,710, filed Aug. 22, 2016, which is a national phaseentry under 35 U.S.C. § 371 of International Application No.PCT/FR2015/050416, filed on Feb. 20, 2015, published in French, whichclaims priority to French Patent Application No. 1451409, filed on Feb.21, 2014, the disclosures of all of which are hereby incorporated hereinby reference.

BACKGROUND OF THE INVENTION

The invention is located in the general field of electronic cigarettescomprising a heating element suitable for vaporizing a substrate inresponse to inhalations by the user, when the heating element ispowered.

More specifically, the invention proposes a solution to provide forestimating the quantity of substrate vaporized by the heating element.

Solutions aiming to estimate this quantity are known, measuring thevariation in the resistivity of the heating element when the temperatureof this heating element varies due to inhalations.

Document EP 2 468 116 describes in particular a solution of this type inwhich the resistivity of a heating element is calculated from thepotential difference across the terminals of this element.

Unfortunately, the variation in the resistivity of the heating elementis very difficult to measure such that these solutions do not providefor accurately estimating the quantity of substrate vaporized.

OBJECT AND SUMMARY OF THE INVENTION

According to a first aspect, the invention relates to a method forestimating the quantity of substrate vaporized by a heating element inan electronic cigarette over a period of smoking.

In this document, the notion of “vaporization” is taken in the broadsense; it denotes the transformation of the substrate into gas,including at a temperature of less than 100° C.

This method includes:

-   -   a step for measuring an approximation of a characteristic of the        voltage across the terminals of the heating element over this        period of smoking, this approximation being measured at the        terminals of a circuit, no component of which exhibits intrinsic        characteristics interfered with by the inhalations;    -   a step for estimating an approximation of this characteristic of        the voltage across the terminals of the heating element in the        absence of inhalation over the period of smoking;    -   a step for calculating an intensity representative of the        inhalations over the period of smoking from an integration of        the difference between said approximations over said period of        smoking; and    -   a step for estimating the quantity of substrate vaporized by the        heating element from this intensity and possibly from other        parameters.

Correspondingly, the invention relates to an electronic cigaretteincluding:

-   -   a heating element suitable for vaporizing a substrate over a        period of smoking, characterized in that it includes:    -   means for measuring an approximation of a characteristic of the        voltage across the terminals of the heating element over this        period of smoking, this approximation being measured at the        terminals of a circuit, no component of which exhibits intrinsic        characteristics interfered with by the inhalations;    -   means for estimating an approximation of this characteristic of        the voltage across the terminals of the heating element in the        absence of inhalation over the period of smoking;    -   means for calculating an intensity of inhalations over the        period of smoking from an integration of the difference between        said approximations over said period of smoking; and    -   means for estimating said quantity of substrate vaporized by the        heating element from this intensity and possibly from other        parameters.

Thus, and generally, the invention proposes estimating the quantity ofsubstrate vaporized over a period of smoking, by comparing thecharacteristics of the voltage across the terminals of the heatingelement with these characteristics in the absence of inhalation.However, very advantageously, the invention does not directly measurethese characteristics, but measures estimates at the terminals of acircuit, the intrinsic characteristics of which are not interfered withby the inhalations.

By virtue of this particularly advantageous feature, the inventionprovides for very reliably estimating the intensity of theseinhalations, and therefore considerably improving the estimate of thequantity of substrate vaporized.

Very advantageously, the abovementioned circuit, in which measurementsare carried out at its terminals in order to estimate thecharacteristics of the voltage across the terminals of the heatingelement, does not itself include any heating element. This featureadvantageously provides for limiting the power consumed for thedetection of the quantity of substrate vaporized, such that a very largemajority of the total power consumed by the electronic cigarette is usedto vaporize the substrate. The device of the invention to measure thequantity of substrate vaporized by an electronic cigarette thereforedoes not exhibit the drawbacks of the device described in document EP 2143 346.

In one embodiment of the invention, the determined quantity of substratevaporized is used to estimate the quantity or quality of componentsinhaled by the user, for example a quantity of nicotine.

In a first variant embodiment of the invention, the variation in thevoltage across the terminals of the heating element is estimated.

In a first embodiment of this first variant, an approximation of thevariation in the voltage across the terminals of the heating element iscalculated from voltages measured at the terminals of at least twoelements, the voltages across the terminals of each of these elementsgiving an approximation of the voltage across the terminals of theheating element at instants that are slightly shifted in time.

In this embodiment of the invention, the electronic cigarette accordingto the invention includes:

-   -   at least two elements, the voltage across the terminals of each        of said elements giving an approximation of the voltage across        the terminals of said heating element at instants that are        slightly shifted in time, and    -   means for measuring an approximation of the variation in the        voltage across the terminals of the heating element from the        voltages measured at the terminals of said elements.

The invention provides for following the change over time of thecharacteristics of the voltage across the terminals of the heatingelement, not with the aid of a tool which would precisely and directlyfollow this voltage in real time, but by creating an artificial delaydelta between two elements of the electronic cigarette, this delayproviding for obtaining at an instant t an estimate of the change involtage across the terminals of the heating means between the instantt-delta and the instant t.

In one embodiment, these elements are series RC circuits connected inseries.

In a second embodiment of this first variant, the approximation of thevariation in the voltage across the terminals of the heating element isthe time derivative of a potential difference measured at the terminalsof a measurement resistance connected in series with the heatingelement.

In a second variant embodiment of the invention, the voltage across theterminals of the heating element is estimated.

In one embodiment of this second variant, the approximation of thevoltage across the terminals of the heating element is the voltagemeasured at the terminals of a measurement resistance connected inseries with said heating element.

In this embodiment, the electronic cigarette includes means suitable formeasuring a potential difference across the terminals of a measurementresistance connected in series with the heating element, and means formeasuring an approximation of the variation in the voltage across theterminals of the heating element from said potential difference.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will emerge fromthe description given below, with reference to the accompanying drawingswhich illustrate an example embodiment thereof lacking any limitingcharacter. In these drawings:

FIG. 1 represents a first embodiment of an electronic cigarette inaccordance with the invention;

FIG. 2 represents the variation in voltage across the terminals ofvarious components of the electronic cigarette of FIG. 1 following aninhalation;

FIG. 3 represents the theoretical difference between the output voltagesof two RC circuits of FIG. 1, in the absence of inhalation;

FIG. 4 illustrates a method for calculating an intensity of inhalationin the electronic cigarette of FIG. 1;

FIG. 5 represents details of an electronic cigarette in accordance witha second embodiment of the invention;

FIG. 6 represents details of an electronic cigarette in accordance witha third embodiment of the invention;

FIG. 7 illustrates a method for calculating an intensity of inhalationin the electronic cigarette of FIG. 6; and

FIG. 8 represents details of an electronic cigarette in accordance witha fourth embodiment of the invention;

FIG. 9 represents, in the form of a flow chart, the main steps of anestimating method in accordance with a particular embodiment of theinvention.

DETAILED DESCRIPTION OF A FIRST EMBODIMENT OF THE INVENTION

There will now be described, with reference to FIG. 1, a firstembodiment of an electronic cigarette 1 in accordance with theinvention, in which figure only the electronic components useful to theunderstanding of this embodiment have been represented.

The electronic cigarette 1 includes a heating element 10 suitable forvaporizing a substrate, the resistivity R10(t) of this heating elementbeing capable of varying as a function of its temperature.

In this embodiment, the heating element 10 includes a first terminal,not referenced, connected to ground and a second terminal A, such thatthe potential U10 of this terminal corresponds to the voltage across theterminals of the heating element 10.

In accordance with the invention, the electronic cigarette 1 includes abattery 3 suitable for delivering a voltage U0, and a switch 5 connectedto a terminal P of the battery, in order to power, only when the userpresses a button, not represented, the heating element 10 from thebattery 3.

In the embodiment described here, the voltage U0 exhibits a nominalvoltage of the order of 3.7 V and a discharge curve in a range [4.2 V, 0V].

When the switch 5 is in the closed position, an electrical current ofintensity i passes through this switch and an electrical current ofintensity i10 passes through the heating element 10.

So as to be able to measure the variations in the voltage U10(t) acrossthe terminals of the heating element 10, the electronic cigarette 1includes, in this embodiment, a measurement resistance R placed inseries between a terminal Q of the switch 5 and the terminal A of theheating element 10. The electrical current of intensity i passes throughthe measurement resistance when the switch 5 is in the closed position.The intrinsic characteristics of the measurement resistance R are notinterfered with by the inhalations.

Due to this particular arrangement, and considering that the switch 5 isa perfect switch (i.e. lossless, therefore U5=U0), the following isobtained in a known manner:U10(t)=U0·R10(t)/(R+R10(t))  (1)

Consequently, variations in the resistivity R10(t) of the heatingelement 10 are accompanied by a variation in the voltage U10(t) acrossthe terminals of the heating element.

FIG. 2 represents on the ordinate the voltage U10(t) across theterminals of the heating element 10 as a function of time, in whichfigure four events occurring at instants t1 to t4 have been represented:

-   -   t1: press of the button closing the switch 5. The voltage U10(t)        across the terminals of the heating element 10 which was zero        almost instantaneously reaches a voltage very close to the        voltage U0 of the battery 3. From this instant t1 and as long as        the user does not inhale, the temperature of the heating element        10 increases until it reaches a limit temperature, its        resistivity R10(t) increases and the voltage U10(t) increases.    -   t2 and t3: start and stop of inhalation. Inhalation brings a        flow of cold air over the heating element 10 having the effect        of lowering its temperature, reducing its resistivity R10(t) and        therefore lowering the voltage U10(t) across its terminals.        Conversely, the end of the inhalation brings about, if the        switch 5 is held closed, a reheating of the heating element and        an increase in the voltage across its terminals.    -   t4: release of the button and opening of the switch 5: the        heating element 10 is no longer powered by the battery 3 and the        voltage U10(t) across its terminals becomes zero again almost        instantaneously.

In this document, “period of smoking” refers to the time period betweenthe instants t1 and t4, i.e. the period over which the user presses thebutton commanding the switch 5 into the closed position. During thisperiod, the user can if necessary not inhale, or inhale one or severalpuffs.

In this first particular embodiment of the invention, the quantity ofsubstrate vaporized over a period of smoking is estimated by comparing ameasurement ΔU10_(MES)(t) of an approximation of the variation in thevoltage U10(t) across the terminals of the heating element 10 over thisperiod of smoking with a theoretical estimate ΔU10_(TH)(t) of thisapproximation of this variation in voltage in the absence of anyinhalation over this period of smoking.

More specifically, in this embodiment of the invention, there is chosen,as an approximation of the variation in voltage at instant t across theterminals of the heating element 10, the difference between two voltagesU11(t) and U12(t) measured at the terminals B1, B2 of a circuit 500comprising two subcircuits 11, 12 that are distinct and of the sametype, the voltages U11(t) and U12(t) across the terminals of thiscircuit 500 being approximations of the voltage U10(t) across theterminals of the heating element 10 at two instants that are slightlyshifted in time.

It is fundamental to observe that none of the components of the circuit500 has intrinsic characteristics interfered with by the inhalations.

In the embodiment described here, two series RC subcircuits 11, 12 areused, placed in series between the heating element 10 and calculationmeans 30 suitable for calculating the difference between the voltagesU11(t) and U12(t).

In the embodiment described here, the voltages U11(t) and U12(t) are thepotentials of points B and C represented in FIG. 1.

The time constant T12 of the second RC circuit 12 is chosen to be muchgreater than the time constant T11 of the first RC circuit 11, forexample by a factor of 100.

In the embodiment described here, an amplifier 20 of gain G is used toamplify the difference ΔU10(t) between U11(t) and U12(t).

In the embodiment described here, the resistances R11 and R12 of the RCsubcircuits 11 and 12 are negligible with respect to the impedance ofthe amplifier 20.

Consequently,ΔU10(t)=G·(U12(t)−U11(t))

In the embodiment described here:

-   -   the gain G is chosen to be in the range [100; 10000], for        example equal to 500;    -   the difference U12(t)−U11(t) is of the order of a few tens of        microvolts; and    -   ΔU10(t) is of the order of a few tens, even hundreds, of        microvolts, and can be measured by the calculation means 30.

In FIG. 2, the output voltages U11(t) and U12(t) of the series RCsubcircuits 11 and 12 are also represented.

As explained previously, when the user presses the button at instant t1,the heating element 10 is powered and the voltage U10(t) across itsterminals increases. The two capacitances C11, C12 of the RC subcircuits11, 12 charge up, the second and higher-value capacitance C12 being indelay with respect to the first and lower-value capacitance C11.Consequently, it is observed between pressing the button (t1) andstarting inhalation (t2) that U12(t)<U11(t)<U10(t).

When the user starts to inhale at instant t2, the heating element 10cools and the voltage U10(t) across its terminals reduces. The secondand higher-value capacitance C12 is in delay with respect to the firstand lower-value capacitance C11. It is observed over the entire durationof the inhalation, i.e. between t2 and t3, that U12(t)>U11(t)>U10(t).

When the user stops inhaling at instant t3, the heating element 10 heatsup again and the voltage U10(t) across its terminals increases. There isthen a return to the situation in which: U12(t)<U11(t)<U10(t).

Shortly after the user releases the button at instant t4, the voltageU10(t) becomes zero again, the capacitances C11 and C12 discharge andtheir output voltages U11(t), U12(t) become zero again.

In a known way, a distinction is drawn, when a constant voltage isapplied across the terminals of a capacitance, between a transient stateduring which the capacitance charges up gradually until it reaches alimit charge depending on its value, and a steady state during which thecharge of the capacitance remains at this limit value as long as thisconstant voltage is continued to be applied to it.

FIG. 2 corresponds to the situation in which the user begins to inhale(instant t2) in the steady state. The person skilled in the art willunderstand that if the user began to inhale during the transient state,since the high-value capacitance C12 is not completely charged, theoutput voltage U12(t) of the second capacitance would not necessarilybecome greater than the output voltage U11(t) of the first capacitance.

In the embodiment described here, the system formed by the twosubcircuits 11 and 12 is in the transient state for about 800 ms afterinstant t1 at which the user presses the button.

FIG. 3, which represents the theoretical difference ΔU10_(TH)(t) betweenthe output voltages U11(t) and U12(t) of the two RC subcircuits 11, 12in the absence of inhalation, in other words a theoretical approximationof the variation in the voltage U10(t) across the terminals of theheating element 10 at the instant t, illustrates these different states.

During the transient state, U12(t) is always less than U11(t) but, asrepresented in FIG. 2, the absolute value of the difference betweenthese two voltages increases then decreases until it reaches a constantvalue a in the steady state.

In the embodiment described here, this constant α can be neglected andis assumed to be zero hereafter.

In the transient state, and noting:

-   -   R11, the resistance of the first series RC subcircuit 11;    -   C11, the capacitance of the first series RC subcircuit 11;    -   R12, the resistance of the second series RC subcircuit 12;    -   C12, the capacitance of the second series RC subcircuit 12;    -   T11, the time constant R1·C1 of the first series RC subcircuit        11; and    -   T12, the time constant R2·C2 of the second series RC subcircuit        12; the following is theoretically obtained:        U11_(TH)(t)=U10(t)·(1−exp(−t/T11))        U12_(TH)(t)=U11_(TH)(t)·(1−exp(−t/T12))        i.e. U12_(TH)(t)=U10(t)·(1−exp(−t/T11))·(1−exp(−t/T12))

Consequently, the theoretical variation ΔU10_(TH)(t) in the voltageacross the terminals of the heating element 10 is expressed as:ΔU10_(TH)(t)=G·(U11_(TH)(t)−U12_(TH)(t))i.e. ΔU10_(TH)(t)=G·U10(t)·(1−exp(−t/T11))·(exp(−t/T12))or with (1):ΔU1O _(TH)(t)=G·[U0·R10(t)/(R+R10(t))]·(1−exp(−t/T11))·(exp(−t/T12))

By making the approximation that R10(t) is constant over the period ofsmoking and equal to R10(t1), the expression for ΔU10_(TH)(t) is finallyobtained:

-   -   in the transient state:        ΔU1O        _(TH)(t)=G·[U0·R10(t1)/(R+R10(t1))]·(1−exp(−t/T11))·(exp(−t/T12))  (2)    -   in the steady state:        ΔU10_(TH)(t)=α=0.

In the embodiment of FIG. 1, the approximation ΔU10_(MES)(t) of thevariation in the voltage U10(t) across the terminals of the heatingelement 10 is the output voltage of the amplification means 20, i.e. thepotential of the terminal 9.

In the embodiment described here, the quantity of substrate vaporizedover a period of smoking is estimated from an intensity of inhalation Fcalculated by integrating the difference over a period of smoking,between the approximation ΔU10_(MES)(t) of the variation in the voltageU10(t) across the terminals of the heating element 10 over this periodof smoking and the theoretical estimate ΔU10_(TH)(t) of thisapproximation of this variation in voltage in the absence of anyinhalation over the period of smoking.

This intensity of inhalation F corresponds, in the example embodimentdescribed here, to the hatched area in FIG. 4. This area can notably becalculated by a Riemann sum with an interval of 20 ms between theinstants t2 and t4.

In the example embodiment described here, t2 is determined as being theinstant at which the absolute value of the difference ΔU10_(MES)(t) andΔU10_(TH)(t) becomes greater than a predetermined threshold S_(T2):|ΔU10_(MES)(t2)−ΔU10_(TH)(t2)|>S _(T2)

Instant t4 is the instant at which the user releases the button.

To calculate the intensity of inhalation F by the Riemann method,ΔU10_(MES)(t) and ΔU10_(TH)(t) are evaluated and stored at variousinstants between t1 and t4, for example every 20 ms. In this embodiment:

-   1. ΔU10_(MES)(t) is the measurement of the potential of the terminal    9 at instant t;-   2. ΔU10_(TH)(t) between t1 and t1+800 ms (transient state) is read    from a record of a first database BD1 constructed during preliminary    tests carried out in the laboratory and stored in the electronic    cigarette 1, the record being selected as a function of the    parameters of equation (2).-   3. ΔU10_(TH)(t)=0, between t1+800 ms and t4 (steady state).

Returning to equation (2), the expression for ΔU10_(TH)(t) in thetransient state is dependent on six parameters, namely:

-   -   the gain G of the amplifier 20;    -   the voltage U0 delivered by the battery 3;    -   the resistivity R10(t1) of the heating element assumed to be        constant;    -   the value of the measurement resistance R;    -   the time constants T11 and T12 of the RC subcircuits 11 and 12.

In the embodiment described here, and returning to FIG. 1, thecalculation means 30 are suitable for measuring the voltage U0 at theterminal P of the battery 3 by means of a voltage probe 6.

In the embodiment described here, the calculation means 30 are alsosuitable for estimating the resistivity R10(t1) of the heating element.To this end, the calculation means 30 measure, at instant t1, thevoltages U5 at the terminal Q of the switch 5 by means of a voltageprobe 7 and the voltage U10 at the terminal A of the heating element 10by means of a voltage probe 8.

Denoting by i the intensity of the electronic current which flowsthrough the resistance R, application of Kirchhoff's current law at theterminal A and Ohm's law to the resistance R gives rise to:i1+i10=(U5−U10)/R.

However, in the embodiment described here, i1 is negligible next to i10.Consequently, by application of Ohm's law to the heating element 10:R10=R·U10/(U5−U10)  (3)

In the embodiment of the invention described here, the first databaseBD1 stores, for a plurality of sextuples corresponding to the sixparameters {G, U0, R10, R, T11, T12}, values of the theoretical voltageΔU10_(TH)(t) in the absence of inhalation and in the transient state atvarious instants t counted between t1 and t1+800 ms.

The calculation means are therefore capable of calculating the intensityof inhalation F by the Riemann method.

In the embodiment described here, the calculation means 30 query asecond database BD2 of the electronic cigarette 1 in order to determinethe quantity of substrate vaporized over the period of smoking as afunction of four parameters:

-   -   duration t4-t1 of the period of smoking;    -   voltage U0 of the battery 3 measured by the calculation means        30;    -   resistance R10(t1) of the heating element 10, assumed to be        constant over a period of smoking, and measured by the        calculation means 30; and    -   intensity of inhalation F, calculated here by the Riemann        method.

As a variant, other parameters can also be used and notably thetemperature of the heating element 10 at t1, the viscosity of thesubstrate, the speed of evaporation of the substrate, the transferfunction of the heating element 10 characterizing its cooling, thedensity of drops of substrate vaporized as a function of the intensityof inhalation F, etc.

In the embodiment described here, the voltage U0 of the battery 3 ismeasured by the calculation means 30. As a variant, this voltage couldbe considered to be constant and equal to the nominal value of thebattery.

DESCRIPTION OF A SECOND EMBODIMENT OF THE INVENTION

In the embodiment of FIG. 1, two series RC subcircuits 11, 12 in seriesand an amplifier 20 are used to estimate the variation in voltageΔU10(t) across the terminals of the heating element 10.

As a variant, and as represented in FIG. 5, a circuit 500 can, forexample, be used, comprising three RC subcircuits and two amplifiers 20₁, 20 ₂.

In this embodiment:

-   -   the first RC subcircuit (R11/C11) very closely follows the        voltage across the terminals of the heating element R10 and        represents an estimate of the voltage across the terminals of        the heating element R10(t) at instant t of the measurement;    -   the second RC subcircuit (R12/C12) follows with a slight delay        dt the voltage across the terminals of the heating element R10        and represents an estimate of that which was the voltage        R10(t−dt) across the terminals of the heating element R10 at a        past instant t−dt close to instant t of the measurement;    -   the third RC subcircuit (R13/C13) follows with a more        significant delay Dt the voltage across the terminals of the        heating element R10 and represents an estimate of that which was        the voltage R10(t−Dt) across the terminals of the heating        element R10 at a past instant t−Dt further away from instant t        of the measurement.

To this end, the time constants of the three RC subcircuits are chosensuch that the following expression is satisfied:R11·C11<R12·C12<R13·C13;

Furthermore, for a finer tracking, it may be more optimal toadditionally have the following expression satisfied:(R11·C11)/(R12·C12)<(R12·C12)/(R13·C13)

None of the components of the circuit 500 have intrinsic characteristicsinterfered with by the inhalations.

In this embodiment, the circuit 500 exhibits four terminals B1, B2, B3and B4.

As in the first embodiment, the quantity of substrate vaporized over aperiod of smoking is estimated from an intensity of inhalation Fcalculated by integrating the difference over a period of smoking,between the approximation of the variation in the voltage U10(t) acrossthe terminals of the heating element 10 over this period of smoking andthe theoretical estimate ΔU10_(TH)(t) of this approximation of thisvariation in voltage in the absence of any inhalation over the period ofsmoking.

However, very advantageously, in this embodiment, two approximationsΔU10¹ _(MES)(t) and ΔU10² _(MES)(t) of the variation in the voltageU10(t) across the terminals of the heating element 10 over the period ofsmoking are carried out, the first approximation being measured at theterminals B1 and B2 of the circuit 500, and the second approximationbeing measured at the terminals B3 and B4 of the circuit 500.

This embodiment provides for improving the estimate of the variations involtage across the terminals of the heating element 10, and thisregardless of the characteristics of the puff.

Indeed, by virtue of the choice of the time constants:

-   -   the voltage measured at the terminals B1 and B2 of the circuit        500 is particularly representative of the voltage across the        terminals of the heating element R10 for a certain type of        inhalation, for example a fast and/or intense or irregular        inhalation; while    -   the voltage measured at the terminals B3 and B4 of the circuit        500 is particularly representative of the voltage across the        terminals of the heating element R10 for another type of        inhalation, for example a slow and/or light or continuous        inhalation.

Hence, in this embodiment, the following two curves ΔU10_(MES)(t) andΔU10_(TH)(t) are constructed:ΔU10_(MES)(t)=K1ΔU10¹ _(MES)(t)+K2ΔU10² _(MES)(t)ΔU10_(TH)(t)=K1ΔU10¹ _(TH)(t)+K2ΔU10² _(TH)(t)where ΔU10¹ _(TH)(t) and ΔU10² _(TH)(t) are theoretical estimates ofapproximations ΔU10¹ _(MES)(t) and ΔU10² _(MES)(t) in the absence of anyinhalation over the period of smoking.

Hence, to calculate the intensity F of the inhalation, the area betweenthese two curves ΔU10_(MES) and ΔU10_(TH) is retained.

The coefficients K1 and K2 are fixed and determined as a function of thetime constants of the RC circuits (the values R11·C11, R12·C12 andR13·C13).

In a nonlimiting manner, this pair of coefficients could be chosen inaccordance with one of the four following examples:

Example 1

K1=½; K2=½

Example 2

K1=(R11·C11+R12·C12)/(R11·C11+2·R12·C12+R13·C13);K2=(R12·C12+R13·C13)/(R11·C11+2·R12·C12+R13·C13)

Example 3

K1=R12·C12/(R11·C11)/((R12·C12)/(R11·C11)+(R13·C13)/(R12·C12));K2=R13·C13/(R12·C12)/((R12·C12)/(R11·C11)+(R13·C13)/(R12·C12))

Example 4

K1=(R12·C12−R11·C11)/(R13·C13−R11·C11);K2=(R13·C13−R12·C12)/(R13·C13−R11·C11)

To ensure correct operation, these coefficients can be tested/validatedin the laboratory.

DESCRIPTION OF A THIRD EMBODIMENT OF THE INVENTION

In the embodiment of FIG. 6, the variable for the voltage across theterminals of the heating element which is estimated is not the variationΔU10(t) of this voltage but the value U10(t) of this voltage itself.

In this embodiment of the invention, this value U10(t) is estimated bymeasuring the voltage U5−U10 across the terminals B1 and B2 of a circuit500 formed in this example by the measurement resistance R.

Specifically, from equation (3):U10(t)=R10/R·(U5−U10)(t)  (4)

This embodiment requires the calculation means 30 to be connected to theterminals B1 and B2 of the measurement resistance R in order toprecisely measure the variations of U5-U10.

FIG. 7 represents:

-   -   the approximation U10_(MES)(t) of the voltage U10(t) across the        terminals of the heating element 10 over the period of smoking,        calculated by using equation (4), the difference of (U5−U10)(t)        being the difference of the potentials measured by the        calculation means 30 of FIG. 6 between the points B1 and B2;    -   the estimate of the approximation U10_(TH)(t) across the        terminals of the heating element 10 in the absence of inhalation        over said period of smoking;    -   the intensity F of the inhalation corresponding to the        integration of the difference between U10_(MES)(t) and        U10_(TH)(t) over the period of smoking.

DESCRIPTION OF A FOURTH EMBODIMENT OF THE INVENTION

In a fourth embodiment represented in FIG. 8, in order to estimate thevariation ΔU_(MES)10(t) in the voltage across the terminals of theheating element 10, as for the first embodiment, the difference betweentwo voltages U12(t) and U11(t) at the terminals B1 and B2 of a circuit500 is executed, each of these voltages giving an approximation of thevoltage across the terminals of the heating element (10) at instantsthat are slightly shifted in time.

In this embodiment, to generate this delay, a circuit 500 is used,formed by a delay line 90 between the measurement points for thevoltages U11(t) and U12(t).

This delay line can for example be formed by:

-   -   a large capacitance;    -   an analog-digital converter coupled to a digital-analog        converter.

The intrinsic characteristics of the delay line 90 are not interferedwith by the inhalations.

DESCRIPTION OF A FIFTH EMBODIMENT OF THE INVENTION

In a fourth embodiment of the invention, the variation ΔU_(MES)10(t) inthe voltage across the terminals of the heating element 10 can also beestimated, by calculating the time derivative of the measured voltageU10_(MES)(t), as in the third embodiment, with the calculation means 30of FIG. 6 between the points B1 and B2.

This value can be compared with the theoretical variation ΔU_(TH)10(t)of the voltage across the terminals of the heating element 10 in theabsence of inhalation, as in the first embodiment.

FIG. 9 represents in the form of a flow chart a method for estimatingthe quantity of substrate vaporized in accordance with a particularembodiment of the invention.

This method can for example be implemented by the calculation means 30of the electronic cigarette of FIG. 1.

During a step E10, the calculation means 30 detect the press of thebutton bringing about the closure of the switch 5. Instant t1 of thisdetection is saved in memory.

During a step E20, just after this detection, the calculation means 30measure the voltage U0 delivered by the battery 3 and the resistivityR10(t1) of the heating element.

Every 20 ms, during a step E30, until instant t4 of detection of therelease of the button bringing about the opening of the switch 5, thecalculation means 30:

-   -   measure ΔU10_(MES)(t) (potential of the terminal 9);    -   estimate ΔU10_(TH)(t) by reading the first database BD1 between        t1 and t1+800 ms. Between t1+800 ms and t4, they estimate        ΔU10_(TH)(t)=0.

During a step E40, the calculation means 30 estimate instant t2 of thestart of the puff, this instant being the first instant after t1 suchthat |ΔU10_(MES)(t2)−ΔU10_(TH)(t2)|>S_(T2).

During a step E50, the calculation means 30 calculate the intensity F ofthe inhalation as the integration of the difference betweenΔU10_(MES)(t) and ΔU10_(TH)(t) between t2 and t4.

During a step E60, the calculation means 30 estimate the quantity ofsubstrate vaporized between t2 and t4 by querying the second databaseB2.

The invention claimed is:
 1. A method of estimating a start time of aninhalation in an electronic cigarette, the method comprising:determining an approximation of a characteristic of a voltage acrossterminals of a heating element of the electronic cigarette over a periodof smoking, the approximation being measured at terminals of a circuitconnected to the heating element, no component of which exhibitsintrinsic characteristics interfered with by the inhalation; estimatingan approximation of the characteristic of the voltage across theterminals of the heating element in an absence of the inhalation overthe period of smoking; estimating the start time of the inhalation bycomparing a difference between the approximations over the period ofsmoking to a predetermined threshold.
 2. The method as claimed in claim1, wherein the characteristic of the voltage is a voltage at a giveninstant or a variation of a voltage at a given instant.
 3. The method asclaimed in claim 2, wherein the approximation of the variation of thevoltage across the terminals of the heating element is calculated fromvoltages measured at the terminals of at least two elements, thevoltages across the terminals of each of the at least two elementsproviding an approximation of the voltage across the terminals of theheating element at instants that are slightly shifted in time.
 4. Themethod as claimed in claim 3, wherein the at least two elements areseries RC circuits connected in series.
 5. The method as claimed inclaim 2, wherein the approximation of the variation of the voltageacross the terminals of the heating element is the time derivative of apotential difference measured at the terminals of a measurementresistance connected in series with said heating element.
 6. The methodas claimed in claim 1, wherein the approximation of the characteristicof the voltage across the terminals of the heating element is determinedfrom a voltage measured at the terminals of a measurement resistanceconnected in series with the heating element.
 7. The method as claimedin claim 1, wherein the start time of the inhalation is estimated to bean instant in time at which an absolute value of the difference betweenthe approximations becomes greater than the predetermined threshold. 8.An electronic cigarette including a heating element suitable forvaporizing a substrate over a period of smoking, the electroniccigarette comprising: means for determining an approximation of acharacteristic of a voltage across terminals of a heating element overthe period of smoking, the approximation being measured at terminals ofa circuit connected to the heating element, no component of whichexhibits intrinsic characteristics interfered with by an inhalation;means for estimating an approximation of the characteristic of thevoltage across the terminals of the heating element in an absence of theinhalation over the period of smoking; means for estimating a start timeof the inhalation by comparing a difference between the approximationsover the period of smoking to a predetermined threshold.
 9. Theelectronic cigarette as claimed in claim 8, wherein the characteristicof the voltage is a voltage at a given instant or a variation of avoltage at a given instant.
 10. The electronic cigarette as claimed inclaim 8, further comprising: at least two elements, a voltage across theterminals of each of the at least two elements providing anapproximation of the voltage across the terminals of the heating elementat instants that are slightly shifted in time; and means for calculatingan approximation of a variation in the voltage across the terminals ofthe heating element from the voltages measured at the terminals of theat least two elements.
 11. The electronic cigarette as claimed in claim10, wherein the at least two elements are series RC circuits connectedin series.
 12. The electronic cigarette as claimed in claim 8, furthercomprising: calculation means configured to determine a potentialdifference across the terminals of a measurement resistance connected inseries with the heating element; and means for determining anapproximation of a variation in the voltage across the terminals of theheating element from the potential difference.
 13. The electroniccigarette as claimed in claim 8, wherein the start time of theinhalation is estimated to be an instant in time at which an absolutevalue of the difference between the approximations becomes greater thanthe predetermined threshold.